The present invention relates to a composition in the form of an aqueous solution of a compound of a preservative metal and certain organic acids solubilized by means of ammonia or an ammonium compound. The invention also relates to the use of such a composition for the preservation of porous materials, particularly porous fibrous materials, such as wood, textiles, ropes, cordage and leather. The invention relates still further to the use of these compositions as agricultural of horticultural fungicides.
The value of compounds of cobalt, iron, manganese, nickel and, more particularly, copper and zinc (hereinafter collectively referred to as "preservative metals") as wood preservatives has been known for a long time. The use of such compounds, particularly of copper, as agricultural and horticultural fungicides is also known. In order to apply the copper or other metal compound to wood in a manner suitable for it to act as a wood preservative, it is necessary first to dissolve the compound in a carrier liquid which is capable of penetrating into the wood. It is further necessary, if the resulting wood-preserving effect is to last for an acceptable length of time, that, after treatment and evaporation of the carrier liquid, together with any initial "curing" or fixation period, the metal compound impregnated into the wood should not be able readily to be leached out by the action of water. Many ways of achieving this have been suggested. For example, it has been proposed to use a water-insoluble metal compound which is soluble in an organic solvent, so that, after evaporation of the organic solvent used as carrier, the water-insoluble metal compound remains in the wood. Examples of such compounds are the copper salts of naphthenic acid or of the organic acids produced by the Koch or Oxo processes, such as 2-ethylhexoic acid, 3,3,5-trimethylnonanoic acid or mixtures of such acids available under various trade names, for example Acid 810, Versatic 10 and the Cekanoic acids.
These acids themselves possess some fungicidal and/or insecticidal properties and, although this is much less than that of copper and the other preservative metals, because they are usually present in an amount by weight several times greater than that of the metal, these acids may add usefully to the efficiency of the combination, particularly in cases where there are present fungal species which can tolerate relatively large amounts of copper or other metal. The acid and metal are normally present in a stoichiometric ratio; however, an excess of acid may be present or, where a basic metal compound can be formed, as with zinc, there may be less than one equivalent of acid for each equivalent of metal. Compositions of this type based upon copper naphthenate have been available for commercial use for about 60 years and are the subject of many national standards, such as British Standards 3770 and 5056. Similar materials based on the branched-chain carboxylic acids, such as the 2-ethylhexoic and 3,3,5-trimethylnonanoic acids referred to above, although a more recent development, have also been in commercial use for several years.
Because these materials are used in solution in organic solvent carriers (such as white spirit, paraffin or related aliphatic or aromatic solvents), they penetrate very readily into the wood or other porous material, but, in certain situations, the requirements for effective protection of the timber or other material necessitate impregnation of fluid throughout the whole of the material. Processes achieving this use large volumes of carrier liquid which, because of the cost of such liquids, make the process uneconomic and also can give rise to a fire or health hazard.
These preservative metals, particularly copper, and these acids also have some fungicidal effect when applied to plants and, as when compositions comprising metal and acid are used for the preservation of timber, it is necessary, when treating plants, that the composition should be applied in the form of a solution but that, once applied, the preservative composition should resist leaching by water. However, organic solvents can represent a very serious fire and health hazard when applied freely to plants and, in some cases, may cause damage to the plants. Furthermore, for domestic use, where the compositions may not be stored under ideal conditions and may be mishandled, organic solvents should, where possible, be avoided.
Water is an inexpensive carrier liquid and an alternative way of depositing compounds of copper or other metals in wood in such a manner that they will resist leaching out by water is to prepare a solution of the compound in water in such a manner that, after impregnation into the wood or application to the plant, a chemical change occurs whereby the formerly soluble metal compound is deposited in an insoluble form. One such method involves dissolving the copper or other metal compound in a solution of ammonia or of an ammonium salt, such as ammonium carbonate or bicarbonate, so that, after treatment, the ammonia evaporates, leaving the copper compound in the required water-insoluble form. United Kingdom Patent Specification No. 599,443, for example, describes the solubilization by such methods of copper and zinc salts of naphthenic acids and their derivatives, saturated and unsaturated carboxylic acids containing more than 10 carbon atoms and abietic acid, and their use for the preservation of textile materials. United Kingdom Patent Specification No. 1,379,095 describes the use of "normal", i.e. straight-chain, fatty acids containing from 6 to 11 carbon atoms per molecule (generally caprylic acid) solubilized in this manner for wood preservation and discloses that carboxylic acids containing more than 11 or less than 6 carbon atoms are unsatisfactory, for one reason or another, as wood preservatives.